CEL P0170 and P0172, Bank 1 Too Rich/Fuel Trim. NEED HELP PLEASE! - HondaCivicForum.com


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Old 05-09-2012, 12:10 PM
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Default CEL P0170 and P0172, Bank 1 Too Rich/Fuel Trim. NEED HELP PLEASE!

So my sister is learning to drive and I found this 98 civic lx auto for $2000. I knew about some issues that were easy fixes that I took care of already like a common crack in the header/02 sensor area.

Literally a day after I get it I get a CEL for P0170 Bank 1 Too Rich. Well I do the usual tune up after getting a used car such as:
-changing/gapping spark plugs
-new plug wires
-new air filter
-change engine oil(pennzoil ultra 5w-30)
-new oil filter
-new transmission oil(amsoil ATF)
-new coolant
-new thermostat
-new fuel filter
-new gas cap

*Updates after replacing engine block, bottom end rebuild, and all engine related gaskets*
-Installed fuel pressure gauge, verified good pressure so I know fuel getting to the motor is good(rules out faulty fuel pump, lines, and injectors)
-Car starts up, idles, and drives fine. Same two codes come back on after 50+ miles of driving.


Before engine rebuild:
Every day it's 50/50 with the car starting fine and others being hesitation while starting up like it's bogging or simply just won't start.

And when the car does start it runs like a champ, perfect idle, smooth shifting. But the hard part is always the starting, wheter after a cold start sitting overnight or a warm start after coming back from being in a store. Sometimes it starts perfectly, others not so much.

When it doesn't start I check for spark by pulling each plug wire and testing each one with a new spare spark plug. Sometimes there's spark, sometimes there isn't.

So when I check the plugs after a no start they have excess fuel and that would explain why I get a code for running rich and would also explain why it won't start, too much fuel to ignite.

-I know the main relay isn't bad because it gets fuel.

-I have bought a new distributor because the old one had a stripped bolt that holds the cap to the casing and would have a gap. New distributor has an air tight seal where the cap sits along with a new coil pack and ICM(which was also tested good at a local autozone).

-I also replaced the ignition switch in case it was intermittent.

-All fuses check good, fuel pump primes like normal when you turn it on.

-I have also replaced the fuel regulator and all injectors.

Only thing I have not messed with is the ECU itself. I'm not understanding how a good gas gap, fuel pump, main relay, injectors, fuel pressure regulator, distributor, plugs and wires can still cause the car to run rich.

I also replaced the primary O2 sensor when I replaced the broken header/catalytic converter because I had a CEL for that as well, but not anymore.

I have not touched the secondary O2 sensor that sits AFTER the converter as I don't think there's a problem with that or how it's even related to spark plugs not igniting upon start up.

If this car ever gets running like normal it will last forever with all the new parts I've bought for it.

Please help, I was hopeful all the previous stuff I've done would've fixed it and I'm tired of dealing with this cars start up issues. Remember, sometimes it doesn't get spark on a good new plug and that excess fuel will build up on the plugs that are installed.

I'm thinking the ECU could be bad, but wouldn't something go completely bad instead of being intermittent if it was related to the ECU?

I thought it would be easy getting this car running for her, as she's going to need it for school soon, but it's being a real PIA.

Last edited by inthezoneac; 02-05-2013 at 07:02 PM.
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Old 05-09-2012, 01:27 PM
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Have you check your timing?
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Old 05-09-2012, 02:43 PM
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no...

The lady I bought it from had a receipt from a timing belt change a couple years ago, I ASSUMED everything related to the head/timing belt should be good.
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Old 05-09-2012, 04:37 PM
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There are definitely (at least) two problems with the car. The ECU doesn't consider fuel mixture until after the engine has warmed up. The fuel system of course has nothing to do with the sparks.

So start (or not) with the no-sparking. Check that the distributor is getting power on the black and yellow wire when you crank. It is common for the ignition switch to lose contact. You can check that by pulling the brake handle up and watch that the BRAKE light stays on all the time while cranking. It is powered from the same circuit as the ignition.

For too much fuel, the pressure could be too high. Make sure the compensator vacuum hose on the regulator is hooked up. Use a stock-type regulator not a cheesy adjustable one. Make sure the return line to the tank is not obstructed. The MAP and IAT sensors affect the mixture. One could be out of spec. Check for an "ebay chip" in the IAT wiring and remove it if present.
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Old 05-09-2012, 05:10 PM
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I will check for power at the wires, along with the hand brake light

The car is pretty much bone stock, no ebay chip. The FPR is a brand new from Honda, it is seated/sealed properly, all vacuum lines connected.

As for the MAP sensor, it is all connected to the throttle body, no way to remove it without destroying the rivets. I thought there would be two phillips screws holding it like my 00 ex, but on this 98 lx it's a vertical mounted TB for the d16y7 and the map sensor is pretty much one piece with the throttle body.

I don't think it would be the MAP or IAT as the problems only occur during start up.

thanks for the replies, will look at it tomorrow
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Old 05-10-2012, 04:10 PM
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I've given up on this pos. Now I'm getting misfire on cylinder 3, wire is good, no spark on ANY PLUG I put in for cylinder 3, then I get misfire all cylinders that occasionally comes up.

Then I get the original symptoms of no spark, but I get 12v on the black yellow wire.

And I don't know if this is recent or it's been like this the whole time my hand brake light does not come on when it's pulled up. But when I try to start it the brake light flashes for the second I try to start, then goes off like it should. But it NEVER comes on before I try to start it. In the first or on position, no brake light.

I also looked at the ecu connectors, as they lead up to the firewall, there's some clear tape with a bundle of wires around the loom. I'm not sure wtf is it, if it's even supposed to be like that but this pos is pissing me off.

I drove it today just fine for 20 miles, while I randomly turned it off and started it up just to make sure starting is not an issue. Then I get home and all starting issues raise from hell with a new cylinder 3 issue.

This pos is going to the shop, I had a fuel gauge for the filter and a map sensor coming in, I'm cancelling those.

I fixed all the known issues and these fn little issues are just like an annoying gnat that just won't go away.

thanks for the help though. I'm tired of spending most of my free time after work dealing with this piece just to end up where I started months ago. I know half the stuff I did will help the car in the long run, but for all I know there could be an ecu, wire harness, and engine problem. Too fn tired to keep messing with it.

Last edited by inthezoneac; 05-10-2012 at 04:22 PM.
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Old 02-05-2013, 06:58 PM
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Latest update:

Let me start by saying the biggest problem I had was head lift due to a screwed up block.

Apparently when the last owner had the headgasket replaced, whoever did the job royally screwed up the install.

I had a few head stud threads in the block that were stripped, so anytime it warmed up coolant would leak out behind the block because the back/intake side of the head would lift due to the pressure. This is what was causing my overheating problem.


Basically I had a buddy of mine replace the block, do a bottom end rebuild and now the engine is functioning properly. It starts up fine and idles fine, engine runs like new.


My problem is that I still get CEL P0170 and P0172 about a day or two after clearing the code.

I even added a fuel pressure gauge on the filter, I'm getting good fuel pressure so I know it rules out a faulty fuel pump, bad lines, or bad injectors.

I downloaded a factory service manual with a step by step guide how to fix this and everything I've done has checked good.

And I know the manual doesn't mention the secondary O2 sensor, but that's probably the only part I haven't replaced relating to the fuel/air system.

Last edited by inthezoneac; 02-05-2013 at 07:05 PM.
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2000, 97, bank, belt, cel, change, civic, fuel, honda, oil, p0170, p0172, rich, system, timing

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